On Tue, Jul 02, 2013 at 12:00:48PM -0700, Paul Berry wrote: > On 28 June 2013 15:39, Chris Wilson <[1]chris at chris-wilson.co.uk> wrote: > > On Fri, Jun 28, 2013 at 03:23:31PM -0700, Ben Widawsky wrote: > > This series originated from the request from Paul, "can you enable > page > > faults"? ?After some though and discussion, we came up with 3 debug > features to > > implement: > > The issue lies in that the CS and EU units like to prefetch 128 bytes > and will cross page boundaries. Userspace is rather lax in providing the > extra page (or preventing the read past the end of its bo) and so > without adding a sentinel page behind every bo you quickly generate > false positives. (Unless you also run a fixed userspace). > > If you are prepared to fix userspace, tweaking the kernel not to install > scratch pages everywhere is trivial. > > Mesa already adds the necessary padding to EU programs to ensure that > prefetch won't cause a page fault, and because of its "stack and heap" > model for batch buffers, CS prefetching shouldn't cause a page fault > either.? I don't know whether the 2D drivers do something similar, so they > might potentially need fixing. You do not on the BLT ring, and have not done historically. The EU is no longer padded. We have been purposely lax in this area. -Chris -- Chris Wilson, Intel Open Source Technology Centre
